Buffering action of human dentin in vitro

Purpose: The purpose of this study was to determine the relative contributions of the mineral and organic phases of dentin to its total buffering capacity and to compare the buffering abilities of normal and cariesaffected dentin for acids used in adhesive dentistry. Materials and Methods: Disks of normal and caries-affected human coronal dentin 0.6 mm thick were prepared. Fifty uL of various acids were applied to the surface of mineralized or completely demineralized dentin for varying lengths of time. They were collected from the surface and combined with water rinses to permit titration of the total amount of acid applied, the amount recovered, the total amount that was taken up by the dentin, and the amount that diffused across dentin into 1 ml of water. Equal volumes of acids were applied to mineralized or demineralized dentin powder or hydroxyapatite powder. Results: About 88% to 90% of applied acid was recovered from the surface; only 10% to 12% of the acid was taken up by dentin. Of the H⁺ that was taken up, only 1% to 2% actually diffused across 0.6 mm of dentin. Increasing the application time of 37% phosphoric acid did not increase the amount of H⁺ that diffused across dentin. Increasing the concentration of phosphoric acid from 10% to 65% produced only slight increases in H⁺ diffusion across dentin. There was no difference in the buffering capacity of normal vs caries-affected dentin disks. Almost all of the buffering capacity of dentin is due to its mineral phase. Conclusion: The high buffering capacity of dentin and the high reactivity of H⁺ insure that little H⁺ diffuses through dentin more than 0.6 mm thick.